In EUTRA LTE-Advanced, carrier aggregation (CA), where multiple component carriers are aggregated and jointly used for transmission and reception within a User Equipment (UE), is introduced to meet the peak data rate requirements of International Mobile Telecommunications (IMT)-Advanced, 1 Gbps and 500 Mbps for downlink and uplink, respectively. Furthermore, CA can provide reduced handover latency and overall, can provide consistent user experience and fairness.
Based on the frequency arrangement of aggregated component carriers (CC), carrier aggregation can be categorized as intra-band contiguous CA, intra-band non-contiguous CA, and inter-band non-contiguous CA. In intra-band contiguous CA, two or more adjacent CCs within a single operating band are aggregated while intra-band non-contiguous CA aggregates non-adjacent CCs in the same frequency band. Inter-band non-contiguous CA aggregates two or more CCs from different frequency bands.
While inter-band CA or intra-band non-contiguous CA allow wireless network operators to effectively utilize the fragmented spectrum, inter-band CA UE may suffer from significant amount of self-interference caused by harmonics of one uplink component carrier from a frequency band falling into another aggregated carrier's receive band or downlink component carrier in another frequency band supported by the inter-band UE. Self-interference may also occur due to intermodulation products of multiple uplink carriers falling into one of its LTE receive bands or receive bands of co-located other radios such as Bluetooth and/or WLAN and/or other cellular networks.
For example in FIG. 1, carrier aggregation scenario 100 of LTE Band 4 and Band 17 aggregation, B and C blocks of lower 700 MHz (uplink: 704-716 102 MHz, downlink: 734-746 MHz 104) and the A block of another spectrum (uplink: 1710-1720 MHz 106, downlink: 2110-2120 MHz 108) may be used together. For the CA capable UE operated in this scenario, the uplink transmission on band 704-707 MHz of Band 17 causes self-desensitization in the downlink band of Band 4 due to the 3rd order harmonic distortion 110, and the almost entire downlink channel band (2112-2120 MHz) in Band 4 can be affected by the harmonic interference. In addition, the harmonic distortion falling into the spectrum near the UE receive band of Band 4 can also cause desense due to potential intermodulation with the received signal.
3GPP RAN working group considers items on inter-band carrier aggregation such as Band 17+Band 4, Band 5+Band 12, Band 5+Band 17, and Band 7+Band 20, the scope of which includes simultaneous activation of two LTE uplink carriers in two bands. Various components at the transceiver path such as antennas, power amplifiers (PAs), connectors, and switches, can contribute to harmonics and intermodulation interference. When two carriers are aggregated with a small frequency separation, the reverse inter-modulation, which is the leakage from one PA output mixed with the input signal of another PA when there is simultaneous transmission on both the carriers, occurs due to co-located PAs for different bands. For example, in uplink CA of Band 5 and Band 12, the 3rd order intermodulation distortion (IMD) falling into the lower Industrial-Scientific-Medical (ISM) band (2400-2414 MHz) can desensitize WLAN and Bluetooth receivers operated in those channels. In 3GPP LTE Rel-11 or future releases, aggregation of more than two component carriers is likely to be supported, and intra-band non-contiguous carrier aggregation may be allowed, which result in more scenarios of self-interference due to intermodulation or harmonics.
Another example of the self-interference is the receiver image interference from adjacent CCs in intra-band contiguous CA 200 is shown in FIG. 2. For the UE supporting multiple contiguous CCs, such as DL CC 1 202 and DL CC 2 204, via a single radio frequency (RF) chain, the receiver image from the adjacent CC may significantly degrade the signal-to-interference and noise ratio (SINR) of the victim CC if the received signal power on the adjacent CC is much higher than the received signal power on the victim carrier. Thus, the received signal power difference between two adjacent CCs which UE can handle is likely to be dependent on UE image rejection capability.
It is expected that self-interference would impact a cell-edge user throughput as the cell-edge UE transmits close to the maximum transmit power while receiving weak downlink signals. However, the mean user throughput is likely not impacted as much. For example, the 5%-tile downlink received signal level is around −70 dBm, which is translated to −98 dBm/15 kHz for a 10 MHz downlink. If the output power of PA is 23 dBm with uplink allocation over 180 KHz, the corresponding 3rd order harmonic response is 7.4 dBm/15 KHz—harmonic suppression capability (in dBc). If the harmonic suppression capability is less than 100 dBc, there will be degradation to the cell-edge user throughput.
Various methods have been developed to reduce the self-interference caused by intermodulation of uplink signals simultaneously transmitted from two different radio access technologies (RAT). These methods disclosed reporting channel quality information (CQI) of the second RAT while the first RAT is active, and at least one subband CQI reported includes potential desense region. However, “fake CQI” (an indication of unusable subband or resource blocks) is reported for the potential desense region without estimating the desense or interference level. Only when UE receives an indicator to report additional CQI reflecting the impact of IMD, the actual CQI can be reported and used by the scheduler.
Considering that each wireless communication terminal operated in a wireless network may have different RF characteristics and performances, applying band/channel combination specific scheduling restrictions at base station schedulers in a consistent manner in order to avoid the self-interference may limit the flexible and effective use of radio resources. Scheduling restrictions also cause extra burden to network equipment vendors due to the increased complexity. Furthermore, in LTE-Advanced carrier aggregation, the potential desense region due to harmonics or IMD may be the entire receive band of one carrier since two wideband LTE channels are aggregated. Therefore, scheduling decision or component carrier management based on the actual self-interference level in each terminal may be beneficial for efficient use of radio resources.
The various aspects, features and advantages of the invention will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. Those skilled in the art will further recognize that references to specific implementation embodiments such as “circuitry” may equally be accomplished via replacement with software instruction executions either on general purpose computing apparatus (e.g., CPU) or specialized processing apparatus (e.g., DSP). It will also be understood that the terms and expressions used herein have the ordinary technical meaning as is accorded to such terms and expressions by persons skilled in the technical field as set forth above except where different specific meanings have otherwise been set forth herein.